This invention relates to the recovery of data from rotating data storage disks such as, typically, compact disks (CDs) used as read-only memories (ROMs) in computer systems. More specifically, the invention concerns how to preclude the possible wobbling of CD-ROMs or the like for error-free reading thereof.
Although originally developed for consumer audio reproduction, CDs have now found widespread acceptance as compact, high-speed, large-capacity ROMs for computers. CD-ROMs are driven at linear velocities several times as high as the standard linear velocities (1.2-1.4 meters per second) of audio CDs.
There has been a problem left unsolved in use of CD-ROMs in high-speed CD-ROM drives in computers. CD-ROMs are made under the same design specifications and manufacturing standards as low-speed audio CDs. Inevitably, therefore, there are some CD-ROMs on the market that are not of satisfactory quality for use as high-speed computer data storage media, including those having their center holes cut eccentrically, and those having an uneven weight distribution circumferentially. Such low-grade disks are easy to wobble when driven at a speed as high as, say, 12 times the standard audio CD speed: The disk wobbling may go so far as to make tracking and focus controls difficult or even impossible. Improper functioning of the tracking and focus controls will result in read errors, which necessitate retries and thus impede high speed data recovery.
The wobbling of low grade disks can give rise to additional inconveniences. A wobbling disk may cause vibration of the complete CD-ROM drive, giving the user a shoddy image. Worse yet, the complete computer may vibrate with the CD-ROM drive. Particularly undesirable is the vibration of a hard-disk drive (HDD) that may be incorporated with the computer along with the CD-ROM drive. The vibration of the HDD can readily lead to read and write errors, to the detriment of the reliability of the computer.
All such troubles and inconveniences might be avoided if only high quality CD-ROMs, altogether free from the physical defects pointed out earlier, were used. CD-ROM drive manufacturers cannot, and should not, expect their products to be used only that way.